The present invention relates to an optical probe and scanning proximity field optical microscope for observing sample surface microscopic geometries and optical properties.
The conventional proximity field optical microscopes have generally used a probe formed by sharpening a tip of a light transmission member such as an optical fiber and coating a portion other than the tip to form a microscopic opening at the tip. The light transmission member principally used an optical fiber. However, if the optical fiber is used as a base material, the transmissible light wavelength is used at approximately 350-1600 nm and inapplicable for observation in a wavelength range of an ultraviolet or infrared portion of light. Furthermore, the metal coating process involves difficulty in manufacture by requiring evaporation while rotating the optical fiber, etc.
Meanwhile, there has been a proposal for an atomic force microscope probe made of silicon or silicon nitride and having a bore formed through a probe needle tip to an opposite surface. Since no light-absorbing solid substance exists within the bore extending from the opening to the backside, a such structure is applicable for observation in an ultraviolet or infrared wavelength range.
The conventional optical probe manufacturing process with an using an optical fiber requires be evaporation to be conducted optical fiber, etc. rotated during the metal coating process, as described above. In such a case, precise control is required for evaporation angle or optical fiber tip form. There is a problem in that if a change is induced, even if slight, it might greatly influence the yield.
The manufacturing process for a type of an atomic force microscope probe having a bore formed therein as described above includes a method of forming a bore through etching and a method of forming a bore using a focused ion beam. The process using etching is used to form a through hole or opening by etching wherein the etching has to be stopped at a certain time. However it is practically impossible to conduct etching while monitoring the formation of such a microscopic opening. As a result, there is extreme difficulty in controlling the size of an opening to be formed. The method using a focused ion beam to form an opening, on the other hand, has a problem in that producibility is low and hence cost of manufacture becomes high. Furthermore, there is another problem in that a bore might be formed in a position than the needle tip due to positional deviation caused by drift of the focused ion beam apparatus.
From these points of view, it is essentially required to provide a proximity field optical microscope having a high controllability in microscopic opening formation in order to utilize the proximity field optical observation technology. There is, as one method for realizing this, a method to use a microscopic opening at a tip of a tube broken by thermal extension as Lewis et al. and Shalone et al. have proposed (U.S. Pat. No. 4,917,462 (1990); Rev. Sci. Instrum. 63 (1992) 4601). In this case, the control of probe-to-sample distance is under STM or shear force control. The use of AFM or STM control poses a problem in that the sample has to possess conductivity. Also, where light is introduced from an end of a tube, the light is required to propagate over a long distance through the inside of the tube resulting in an increase in light loss.
In the case of shear force control, the probe is horizontally vibrated relative to a sample and accordingly usable if the sample has no conductivity. However, simultaneous observation of other physical properties of the sample surface is impossible to conduct despite being possible with the AFM control. The other physical properties referred to herein are friction, viscoelasticity, surface potential, etc. to control the probe by a vertical force onto the sample friction thereby enabling detection. Furthermore, the shear force control method poses a problem in that it requires an on-sample space larger than that of the AFM or STM control method. The reports by Shalone et al. include a bent tube probe for use as an AFM probe. In this case, light is not successfully propagated through the tube bent portion. Accordingly, it is difficult to provide a sufficient amount of light emitted through the bore at the tip.
In order to solve the above problem, the present inventors have devised an optical probe, comprising a tip having a diameter made smaller with respect to an overall diameter; an optically opaque material coated thereon; a tube having an optical microscopic opening formed at a tip thereof; and an optical waveguide having at least two optical end surfaces; wherein the optical waveguide at a one end surface is inserted in an glass tube in a state directed to a microscopic opening.
By making the tube by a glass tube, manufacturing is facilitated. In this case, where using a light with a wavelength transmissible through the glass, light leakage can be prevented by coating at least an outer side of a taper portion with an electromagnetically shielding material such as metal. It is possible to cope with various wavelengths by arbitrarily selecting a corresponding wavelength to the optical waveguide.
Meanwhile, where performing control on a distance between the sample and the probe under atomic force control, if an optical lever is used, detection can be made stably by forming a mirror surface on a tube surface opposite to an opening.
A method for manufacturing an optical probe, includes a method comprising the steps in the order of: (1) elongating and breaking a glass tube; (2) inserting a waveguide; therein and (3) coating with metal, wherein the metal coating is made after the waveguide insertion. Also, a method, comprising the steps in the order of: (1) elongating and breaking a glass tube; (2) coating with metal; and (3) inserting a waveguide, wherein the waveguide is inserted after the metal coating. The latter method of inserting a waveguide after metal coating is superior in mass-producibility because a greater number of probes can be put in a film forming apparatus for metal coating.
Further, a scanning proximity field optical microscope can be structured by at least a light source, a focusing optical system, a relative moving means for causing relative movement between a probe and a sample, a photo detector and the above-mentioned optical probe.